The present invention relates to a waste incineration disposal method.
In recent years, it has been pointed out that dioxins are generated during incineration disposal of a waste. In many cases, the waste contains chlorine. Therefore, when the waste is combusted at a temperature of 250 to 350xc2x0 C., chlorine liberated from the waste, and hydrocarbon generated by incomplete combustion of resins react with each other using a catalyst of a heavy metal contained in the waste, and dioxins are generated.
In order to prevent dioxins emission by the incineration disposal of the waste, it is said to be effective to retain the waste at 800xc2x0 C. or more for two seconds or more, and completely thermally decompose the generated dioxins. However, even when the wastes such as miscellaneous living wastes, paper, and soft vinyl chloride are incinerated, it is difficult to stably keep the wastes at 800xc2x0 C. or a higher temperature. Therefore, in order to prevent the dioxins emission, in general, the wastes are combusted together with other fuels such as a heavy oil, and thereby stably incinerated at 800xc2x0 C. or more. In this case, since the other fuels have to be combusted together with the wastes through the entire incineration disposal process, a large amount of other fuels are required, and a running cost increase cannot be avoided.
Additionally, the present applicant has proposed an apparatus disclosed in Japanese Patent Application Laid-Open No. 135280/1990 as an incineration disposal apparatus of wastes such as a waste tire.
The apparatus disclosed in the above publication is constituted of a fully closed gasification furnace, and a combustion furnace connected to the gasification furnace via a gas passage a part of the waste is combusted in the gasification furnace, and a combustible gas generated by dry distillation of the other part of the waste with the combustion heat is introduced into the combustion furnace to completely combusted the waste. Details of incineration disposal of the waste by the apparatus will next be described.
During the incineration disposal of the waste by the apparatus, first the waste contained beforehand in the fully closed gasification furnace is ignited, a part of the waste is combusted, and the other part thereof is dry-distilled by the combustion heat. Moreover, the combustible gas generated by the dry distillation is introduced into the combustion furnace disposed outside the gasification furnace via the gas passage.
Subsequently, a combustion flame is supplied to the introduced combustible gas to ignite the gas, thereby starting combustion of the combustible gas.
Next, when the dry distillation progresses and the combustible gas is stably generated, an amount of generated combustible gas gradually increases, and a combustion temperature of the combustible gas detected as a temperature T2 in the combustion furnace gradually rises as shown in FIG. 3. In this case, the temperature T2 in the combustion furnace reaches a temperature T2a at which the combustible gas can spontaneously and stably continue the combustion by its own combustion heat, and the supply of the combustion flame is then stopped.
Subsequently, oxygen necessary for complete combustion of the combustible gas is supplied to the combustion furnace in accordance with the amount of the combustible gas introduced into the combustion furnace. Additionally, while the combustible gas is completely combusted, the temperature T2 in the combustion furnace is detected as the combustion temperature of the combustible gas, an amount of oxygen supplied to the gasification furnace is controlled in accordance with a change of temperature T2, and the amount of the combustible gas generated by the dry distillation is adjusted. In the apparatus, the temperature T2 in the combustion furnace can be maintained in this manner to be substantially constant at a temperature T2b higher than a temperature T2a at which the combustible gas spontaneously and stably continues the combustion.
In the apparatus, when the dry distillation further progresses, a portion of the waste able to be dry-distilled in the gasification furnace is reduced. Even when the amount of oxygen supplied to the gasification furnace is increased, a sufficient amount of combustible gas for maintaining the temperature T2 in the combustion furnace to be substantially constant at the temperature T2b cannot be generated Then, the temperature T2 in the combustion furnace gradually drops, the dry distillation and combustion of the waste in the gasification furnace are finished and the waste is ashed. Additionally, a temperature in the gasification furnace is shown as T1 in FIG. 3.
As a result, according to the apparatus, the dry distillation of the waste and the complete combustion of the combustible gas can stably be performed, and in a stage in which the combustible gas spontaneously and stably, continues the combustion, the temperature in the combustion furnace can be maintained to be substantially constant at a preset or higher temperature.
Here, when the apparatus disclosed in the above publication is used in the incineration disposal of the waste, the waste is regulated so as to generate the combustible gas having heat amount for setting a combustion temperature at which dioxins can thermally be decomposed, for example, at 800xc2x0 C. or more. Then, in the stage in which the combustible gas spontaneously and stably continues the combustion, the temperature in the combustion furnace can be maintained to be substantially constant at 800xc2x0 C. or more. Therefore, to keep the temperature in the combustion furnace at 800xc2x0 C. or more, it is unnecessary to combusted other fuels such as a heavy oil, and the dioxins emission can be prevented at a low cost.
However, during the aforementioned waste incineration disposal, in the stage in which the combustible gas spontaneously and stably continues the combustion after the start of the waste dry distillation, and in the stage in which the portion of the waste able to be dry-distilled in the gasification furnace is reduced and the waste is ashed after the stage of the spontaneous and stable continuation of the combustion of the combustible gas, the temperature in the combustion furnace does not reach 800xc2x0 C. and there is a disadvantage that dioxins are emitted.
To solve the aforementioned disadvantage, an object of the present invention is to provide a waste incineration disposal method which can prevent dioxins emission and reduce running costs.
To achieve the aforementioned object, the waste incineration disposal method of the present invention comprises steps of: combusting a part of a waste contained in a gasification furnace, and dry-distilling the other part of the waste by a combustion heat; and introducing a combustible gas generated by the dry distillation into a combustion furnace to combusted the combustible gas. When the combustible gas is combusted in the combustion furnace, oxygen required for the combustion is supplied to the combustion furnace in accordance with an amount of the combustible gas introduced into the combustion furnace to combusted the combustible gas, an amount of oxygen supplied to the gasification furnace is controlled in accordance with a temperature change in the combustion furnace by the combustion of the combustible gas in the combustion furnace, the amount of the combustible gas generated by the dry distillation is adjusted, and the temperature in the combustion furnace is maintained to be substantially constant at a first preset temperature or more. In the waste incineration method, the waste regulated to generate the combustible gas having a heat amount for setting the temperature in the combustion furnace at the first preset temperature or more during the combustion is contained in the gasification furnace. Fuels other than the combustible gas are combusted in the combustion furnace prior to ignition of the waste. When the temperature in the combustion furnace reaches the first preset temperature or more, the waste is ignited to start dry distillation, and the generated combustible gas is combusted with the other fuels. When the temperature in the combustion furnace reaches a second preset temperature higher than the first preset temperature or more by the combustion of only the combustible gas, the combustion of the other fuels is finished, the temperature in the combustion furnace is maintained to be substantially constant at the second preset temperature or more, and only the combustible gas is combusted. When the temperature in the combustion furnace falls below a third preset temperature lower than the substantially constant temperature and higher than the first preset temperature, the combustion of the other fuels is resumed, the combustible gas is combusted with the other fuels, and the temperature in the combustion furnace is maintained at the first preset temperature or more. When the temperature in the gasification furnace falls below a fourth preset temperature lower than a maximum temperature in the gasification furnace, the combustion of the other fuels is finished.
In the method of the present invention, the apparatus disclosed in the aforementioned publication is used, the waste regulated to generate the combustible gas having the heat amount for setting the temperature in the combustion furnace at the first preset temperature or more during combustion is contained in the gasification furnace, and the waste incineration disposal is performed. Here, the first preset temperature is a temperature at which dioxins can thermally be decomposed, and is concretely set at 800xc2x0 C. or more.
In this constitution, when the combustible gas generated by the dry distillation of the waste in the gasification furnace is combusted in the combustion furnace, in the stage in which the combustible gas spontaneously and stably continues the combustion, the other fuels such as a heavy oil are not combusted, the temperature in the combustion furnace is maintained to be substantially constant at 800xc2x0 C. or more by the heat amount of the combustible gas itself and the dioxins emission can be prevented.
Moreover, in the method of the present invention, prior to ignition of the waste, the fuels other than the combustible gas are combusted in the combustion furnace, and the combustion furnace interior is heated at the first preset temperature or more before the combustible gas is introduced into the combustion furnace. Furthermore, when the temperature in the combustion furnace reaches the first preset temperature or more, the waste in the gasification furnace is ignited thereby starting the dry distillation of the waste. As a result, while the temperature in the combustion furnace is not less than the first preset temperature, the combustible gas generated by the dry distillation is introduced into the combustion furnace, and the dioxins emission in the initial stage of dry distillation can be prevented.
In the initial stage of the dry distillation, since the dry distillation is not sufficiently stabilized, the amount of the generated combustible gas is not stable, and it is difficult to maintain the first preset or higher temperature in the combustion furnace by the combustion of only the combustible gas. To solve this problem, in the method of the present invention, the combustible gas is combusted with the other fuels in the initial stage of the dry distillation, and the first preset or higher temperature is thereby maintained in the combustion furnace. Moreover, when the temperature in the combustion furnace reaches the second preset temperature higher than the first preset temperature, or more by the combustion of only the combustible gas, it is judged that the combustible gas can spontaneously and stably continue the combustion, and the combustion of the other fuels is finished. As a result, from the start of the dry distillation until the combustible gas can spontaneously and stably continue the combustion, the dioxins emission can be prevented.
After the combustion of the other fuels is finished, the temperature in the combustion furnace is maintained to be not less than the second preset temperature, that is, to be substantially constant at the first preset temperature or more, and only the combustible gas is combusted. Therefore, as described above, the dioxins emission can be prevented in this stage.
When the waste dry distillation progresses in the gasification furnace and the portion able to be dry-distilled is reduced, the amount of generated combustible gas decreases, and the temperature in the combustion furnace starts dropping from the temperature which is substantially constant at the second preset temperature or more. However, in this stage, the temperature in the gasification furnace is high, and there is still a possibility that dioxins are generated.
To solve the problem, in the method of the present invention, next, when the temperature in the combustion furnace starts dropping from the substantially constant temperature being not less than the second preset temperature, the combustion of the other fuels is resumed at a point at which the temperature falls below the third preset temperature higher than the first preset temperature, so that the temperature in the combustion furnace is not lower than the first preset temperature. When the combustible gas is combusted with the other fuels, the portion of the waste able to be dry-distilled in the gasification furnace is reduced. Even when the amount of the generated combustible gas is reduced, the temperature in the combustion furnace is maintained at or above the first preset temperature.
Moreover, when the temperature in the gasification furnace falls below the fourth preset temperature lower than the maximum temperature in the gasification furnace, it is Judged that the dioxins are not contained in the combustible gas, and the combustion of the other fuels is finished. Here, the fourth preset temperature is concretely set to be less than a dioxins generation temperature. As a result, the dioxins emission can be prevented in the stage in which the portion of the waste able to be dry-distilled in the gasification furnace is reduced and the waste is ashed.
When the combustion of the other fuels is finished, the portion of the waste able to be dry-distilled in the gasification furnace is finally eliminated, the waste is ashed, and extinction naturally occurs. Moreover, even in the combustion furnace, with the decrease of the portion of the waste able to be dry-distilled in the gasification furnace, the amount of the combustible gas is reduced, the spontaneous combustion cannot be maintained, and extinction naturally occurs. As a result, the incineration disposal according to the method of the present invention is naturally finished.
As described above, according to the method of the present invention, from the start of the waste dry distillation until the temperature in the gasification furnace falls below the dioxins generation temperature, the temperature in the combustion furnace is maintained at the first preset temperature or more. Therefore, the dioxins emission can securely be prevented over the entire waste incineration process.
Moreover, in the method of the present invention, in the stage after the waste dry distillation is started and before the combustible gas spontaneously and stably continues the combustion, and in the stage in which the portion of the waste able to be dry-distilled in the gasification furnace is reduced and the waste is ashed after the stage of the spontaneous and stable continuation of the combustion of the combustible gas, the other fuels are combusted. While the combustible gas spontaneously and stably continues the combustion, the other fuels are not combusted. Therefore, the use amount of the other fuels is saved, and the running costs can be reduced.
Moreover, in the method of the present invention, in a period from the waste ignition until the temperature in the combustion furnace reaches the second preset temperature or more by the combustion of only the combustible gas, the combustion of the other fuels is intermittently performed by stopping the combustion of the other fuels when the temperature in the combustion furnace reaches the second preset temperature or more, and again igniting the waste when the temperature in the combustion furnace falls below the second preset temperature after the stop. When the temperature in the combustion furnace is not less than the second preset temperature even after the combustion of the other fuels, the intermittent combustion of the other fuels is finished.
In the method of the present invention, when the combustion of the other fuels is stopped, the temperature in the combustion furnace depends on the combustion of only the combustible gas. Therefore, a combustion state of the combustible gas can be detected by checking the temperature in the combustion furnace after stopping the combustion of the other fuels. Moreover, in the period, when the temperature in the combustion furnace reaches the second preset temperature or more, the combustion of the other fuels is stopped, and the temperature in the combustion furnace then falls below the second preset temperature, it is judged that the temperature in the combustion furnace does not possibly reach the first preset temperature or more by the combustion of only the combustible gas, and the other fuels are ignited again. Furthermore, when the temperature in the combustion furnace reaches the second preset temperature or more after the re-ignition, the combustion of the other fuels is stopped again, and the aforementioned operation is repeated.
Moreover, when the temperature in the combustion furnace is maintained at the second preset temperature or more even after the stop of the combustion of the other fuels, the temperature in the combustion furnace securely reaches the first preset temperature or more by the combustion of only the combustible gas, it is judged that the combustible gas can spontaneously and stably continue the combustion, and the combustion of the other fuels is finished.
Furthermore, in the method of the present invention, in a period from when the temperature in the combustion furnace falls below the third preset temperature until the temperature in the combustion furnace falls below the fourth preset temperature, the combustion of the other fuels is intermittently performed by stopping the combustion of the other fuels when the temperature in the combustion furnace reaches the third preset temperature or more, and again igniting the waste when the temperature in the combustion furnace falls below the third preset temperature after the stop. When the temperature in the combustion furnace falls below the third preset temperature even after the re-ignition, the combustion of the other fuels is continuously performed, and the temperature in the combustion furnace is maintained at the first preset temperature or more. Thereafter, when the temperature in the gasification furnace falls below the fourth preset temperature, the combustion of the other fuels is finished.
In the method of the present invention, when the temperature in the combustion furnace falls below the third preset temperature, the combustion of the other fuels is resumed. Moreover, when the temperature in the combustion furnace reaches the third preset temperature or more by the combustion of the other fuels, the combustion state of the combustible gas can be detected as described above by stopping the combustion of the other fuels and checking the temperature in the combustion furnace after the stop.
Therefore, in the period, when the temperature in the combustion furnace reaches the third preset temperature or more, the combustion of the other fuels is stopped, and the temperature in the combustion furnace falls below the third preset temperature, it is then judged that the temperature in the combustion furnace does not possibly reach the first preset temperature or more by the combustion of only the combustible gas, and the other fuels are ignited again. Moreover, when the temperature in the combustion furnace reaches the third preset temperature or more after the re-ignition, the combustion of the other fuels is stopped again, and the aforementioned operation is repeated.
Furthermore, when the temperature in the combustion furnace falls below the third preset temperature even after the re-ignition of the other fuels, it is judged that the temperature in the combustion furnace cannot be maintained at the first preset temperature or more by the combustion of only the combustible gas, the combustion of the other fuels is continuously performed, and the temperature in the combustion furnace is maintained at the first preset temperature or more. Thereafter, when the temperature in the gasification furnace falls below the fourth preset temperature, as described above, it is judged that the gas introduced into the combustion furnace from the gasification furnace contains no dioxins, and the combustion of the other fuels is finished.
In the method of the present invention, as described above, in the period from the waste ignition until the temperature in the combustion furnace reaches the second preset temperature or more by the combustion of only the combustible gas, or in the period from when the temperature in the combustion furnace falls below the third preset temperature until the temperature in the gasification furnace falls below the fourth preset temperature, the combustion of the other fuels is intermittently performed, so that amount of the other fuels can be saved, and the running costs can be reduced.
Moreover, in the method of the present invention, in a period from when the temperature in the combustion furnace falls below the third preset temperature until the temperature in the gasification furnace falls below the fourth preset temperature, the temperature in the gasification furnace is detected every predetermined time. After it is consecutively detected predetermined times that the temperature in the gasification furnace is less than the maximum temperature in the gasification furnace, and the temperature in the gasification furnace falls below the fourth preset temperature, the combustion of the other fuels is finished.
When the part of the waste able to be dry-distilled is reduced in the gasification furnace, the heat amount consumed in the dry distillation is not consumed, and the temperature in the gasification furnace rapidly starts rising by red heat of the waste. Moreover, when the red heating of the waste is finished and ashing starts, the temperature in the gasification furnace in turn drops from the maximum temperature at which the waste is red-heated.
However, since a material, capacity, and the like of the waste subjected to the incineration disposal by the method of the present invention are various, the red heating does not uniformly shift to the ashing. Even when the surface of the waste is ashed, a lower layer part is still red-heated, and the waste whose red heating is retarded sometimes remains. In this case, the temperature rises again by the red heating of the waste. This tendency becomes more remarkable when the gasification furnace has a large capacity.
Moreover, in the method of the present invention, as described above, the temperature in the gasification furnace is detected every predetermined time, it is consecutively detected predetermined times that the temperature in the gasification furnace is less than the maximum temperature in the gasification furnace, and it is then judged that the waste in the gasification furnace entirely shifts to an ashing stage. Thereafter, when the temperature in the gasification furnace falls below the fourth preset temperature, the combustion of the other fuels is finished. The dioxins emission caused by re-rising of the temperature in the gasification furnace can securely be prevented.
Furthermore, according to the method of the present invention, when the combustible gas generated by the dry distillation of the waste in the gasification furnace is introduced into the combustion furnace and combusted, a part of the combustible gas is dispensed and condensed, and oil content is collected and used as the other fuels.
In the method of the present invention, combustion assistant oils such as a heavy oil can be used as the other fuels. When only the combustion assistant oil is used, however, a burden added by a fuel becomes heavy. Then, the burden can be alleviated by dispensing a part of the combustible gas, and adding the condensed and collected oil content to the other fuels.
In a stage in which the dry distillation progresses well, a sufficient amount of combustible gas is generated to maintain the temperature in the combustion furnace to be substantially constant at the first preset temperature or more. Therefore, even when a part of the combustible gas is dispensed, the temperature in the combustion furnace is not influenced, and the substantially constant temperature is maintained. Moreover, when a combustible component contained in the combustible gas is condensed and liquefied, the component can easily be collected as the oil content.
Moreover, in the method of the present invention, when the other fuels are combusted, oxygen heated by the heat of the combustion furnace is supplied to the combustion furnace.
When heated oxygen is supplied to the combustion furnace, the heat amount consumed by heating oxygen in the combustion furnace is saved, and the combustion temperature of the combustible gas rises. Therefore, when the other fuels are combusted, the fuel can be reduced.